The RDL schemas are different between SSRS 2008 and SSRS 2008 R2.
According to MS you should be able to use Business Intelligence Studio to change the target version of the report to 2008 or 2008 R2 as needed. From this I understand that you will need to match the deployment target with the version of SSRS installed on your production server. See the following link for details
http://msdn.microsoft.com/en-us/library/ee635898.aspx
This MS link describes how you can check the schema used in your report, and the schema available on the server:
http://msdn.microsoft.com/en-us/library/cc627465.aspx
For reference, a a similar issue exists between SSRS2008 and SSRS 2005:
http://mightycode.blogspot.com/2011/03/converting-ssrs-2008-reports-to.html